In radio systems, the quality of a connection between a base station and a subscriber terminal varies constantly due to attenuation and multipath propagation of radiowaves. The attenuation of a signal between a base station and a subscriber terminal is represented by the attenuation on the transmission path, which increases at least quadratically with a growing distance.
An object of power control in a radio system is to enable the base station to receive signals with optimum power levels from the radio path. Another object of power control is to ensure that a subscriber terminal receives from the base station signals which have optimum power levels upon reception.
Prior art base stations and subscriber terminals employ different power control methods. The methods used in linear modulations are not usually optimum due to envelope variations related to the modulation. For example, a power control method utilizing a closed power control loop causes amplitude distortion in the signal to be transmitted, since the signal amplitude is dependent on the transmitted information. Therefore, a problem with prior art transceivers is that the power control loop tends to change the modulated signal that contains information, which possibly leads to loss of information.